CIRCUIT DETECTEUR DE BRUIT ET RECEPTEUR DE SIGNAL POUR UN RECEPTEUR A MODULATION DE FREQUENCE

L'INVENTION CONCERNE LES RECEPTEURS DE SIGNAUX MODULES EN FREQUENCE.UN CIRCUIT DETECTEUR DE BRUIT ET RECEPTEUR DE SIGNAL POUR UN SYSTEME A MODULATION DE FREQUENCE COMPREND NOTAMMENT UN PREMIER CIRCUIT A BOUCLE DE VERROUILLAGE DE PHASE 300 QUI REAGIT AU SIGNAL RECU EN PRODUISANT UN SIGNAL REPRESENTATIF DU NIVEAU DE BRUIT ETEN EFFECTUANT UNE PREMIERE ETAPE DE DEMODULATION DU SIGNAL RECU. UN COMPARATEUR RAPIDE 330 DE LA BOUCLE DE VERROUILLAGE DE PHASE PRODUIT UN SIGNAL DEPHASE DE 90 QUI EST PRATIQUEMENT EN PHASE AVEC LE SIGNAL D'ENTREE, CE QUI AMELIORE LES POSSIBILITES DE DETECTION DE BRUIT DU CIRCUIT A BOUCLE DE VERROUILLAGE DE PHASE.APPLICATION AUX POSTES TELEPHONIQUES DU TYPE "MAINS LIBRES". A noise detector and data signal receiver for a frequency modulation system has a first phaselock loop circuit (300), responsive to the received signal, for providing a signal indicative of the noise level and a first stage of demodulation of the received signal. A high speed comparator (330) of the first phaselock loop circuit provides a 90 degree phase-shifted signal which exhibits lesser delay and is substantially in phase with the input. Accordingly, the noise detection capability of the phaselock loop circuit (300) is improved. A second phaselock loop (200), also responsive to the received signal, extracts a voice signal from the received signal. A third phaselock loop (400) responsive to the once demodulated output signal of the first phaselock loop (300), extracts a digital data signal from the received signal. Squelch circuits (120, 121), activated at separate particular levels of noise, are responsive to the noise level indicator signal of the first phaselock loop. In addition, a noise proportional signal is provided to a speaker for providing the user of a hands-free telephone system of which the present receiver comprises a component with an audible feedback of the noise.